My car doenst idle right - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 03-18-2005, 10:54 PM   #1
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Default My car doenst idle right

I wouldnt describe it as a rough idle or a miss, but the car doesnt quite seem to know where to idle at, when i first start it it idles fine for about 10 or 15 seconds but then you can hear the motor slow down and it will slightly increase boost, im assuming to keep itself started, then it will kick back up for another 10 or 15 seconds, then it will bog down again. It doesnt seem to be too severe, but it is still annoying and i know it isnt right. I have already put a full tune up on it. Could it maybe be a bad coil? I have already scanned the car and everything comes out normal except for the usual stuff, like not wanting to go into closed loop and the QDM B fault that i cant chase down.
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Old 03-18-2005, 10:56 PM   #2
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Check your O2 and clean your TB. Also maybe starting to have a faulty IAC?
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Old 03-18-2005, 10:59 PM   #3
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Ya know thats the second problem that is pointing to a bad 02. and i can swear ive seen that thing act fine one minute when im trying to test it and give me some wacked out bs the next, when im not looking for it. It would be great if this is just a measely little 02 sensor
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Old 03-18-2005, 11:04 PM   #4
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My 95 is pulling the same BS......Except I can get to a closed loop status but will not stay there.....I think my IAC is too slow for the PCM and can't react fast enough and then the o2 just shuts down or something and kicks it out of closed into open loop again. I don't really know how my new Declo o2 sensor could be f'd from this deal when it was fine for about 2 days after I installed it. Nothing but problems since then though.
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Old 03-18-2005, 11:08 PM   #5
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Mine kinda goes in and out of closed loop too, although its out of closed loop a hell of a lot more than its in closed loop.
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Old 03-18-2005, 11:10 PM   #6
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Well try cleaning the TB and the IAC really well and see where that gets ya.
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Old 03-18-2005, 11:16 PM   #7
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What would i clean the iac with
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Old 03-19-2005, 02:16 AM   #8
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I had the same problem, my car would idle quite erratically, ranging from 600-1500 RPM'* if it was bad. Cleaning the IAC fixed that right up. Just use some throttle body cleaner till all the black gunk is gone, and the drip is clean. Then let it dry. Then make some pipe cleaner thing with a clean rag and use some TB cleaner to clean the housing the IAC valve came from. Doesn't take long to do and it is really effective.
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Old 03-19-2005, 04:26 AM   #9
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Interesting cleaning the IAC fixed that, guess it points to the inability of the PCM to compensate. I had a similar issue that turned out to be a vacuum leak of sorts. At idle it was running extremely lean so the PCM was commanding the IAC to close. Then once it got to the point where it was about to stall the PCM commanded the IAC to re-open and keep the engine from dying. The cycle repeated about every 20seconds or so.

jachin - I can't recall if it was A or B but does it only go bad when you press the brakes? I know the scantool Will let me use had an issue and would flip to "bad" when you press the brakes. Not sure if the issue was specific to that model though.
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Old 03-19-2005, 08:34 AM   #10
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Might want to scan the car. Check IAC counts, and short and long term fuel trims. Check all vaccum lines especially under the SC snout and behind the MAP sensor.

Also, you may want to disconnect the MAF sensor to see if it smooths out, make sure you have not removed your TB screen, and check your boost bypass valve to make sure it lays flat when the car is off.
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